1. Field of the invention
The present invention relates first of all to a method of representing, on a given flat support (i.e display device) and in perspective from a given point of observation, the image of a ground terrain known by the coordinates of the nodes of a given mesh network, in which a surface passing through these nodes is determined by interpolation. An assembly of points on the surface is determined and the pixels of the image to be represented, which are associated with this assembly of points, are illuminated so as to display the image on the display device screen.
The invention applies in particular to the presentation, to the pilot of an aircraft, of a synthetic image of the ground terrain over which he is flying or, to the driver of a land vehicle, of a synthetic image of the site in which he is travelling, whatever the conditions of visibility. The invention also makes possible the presentation of images of real or fictitious sites for the purposes of simulation.
In the case of assisting piloting and navigational tasks, the coordinates of the nodes of the mesh network are stored in a memory filled from a data base available for example from the National Geographical Institute. Such a data base contains the altitude of nodes obtained by sampling the terrain every three seconds of an arc, in latitude and in longitude, i.e. about 65 m in latitude and 92 m in longitude for the French territory. The point of observation, as well as the flat support on which the image is represented, depend on the position of the aircraft with respect to the ground, as well as its attitude so that, for example, the image represented corresponds as well as possible to what the pilot may see from his cabin under good conditions of visibility. A processing circuit, connected to the memory storing the coordinates of the nodes of the network and receiving the data from the instruments measuring the position and attitude of the aircraft, then determines the image pixels to be illuminated and consequently controls a display device disposed in front of the pilot.
2. Description of the Prior Art
A method of the above defined type is already known, described in French patent application No. 2 524 177. In this method, the surface determined by interpolation and passing through the nodes includes a set of triangular facets which takes on then approximately the shape of the ground, and the assembly of points of this surface with which the illuminated image pixels will be associated includes the nodes of an auxiliary mesh network, different from the preceding mesh network and depending here on the point of observation. This auxiliary mesh network is projected on a horizontal plane in a set of concentric circles centered on the projection, on the same horizontal plane of the point of observation and in a set of straight lines passing through this projection. In other words, the projection of the auxiliary network on a horizontal plane forms a sort of spider's web centered on the projection of the point of observation. The evenness of this projection of the auxiliary network means that the representation of the nodes of this auxiliary network obtained, by illuminating the image pixels which are associated therewith gives an image of the relief of the facet surface so of the ground to be represented.
However, although this method makes it possible to display the relief of the ground, it gives little information about the corresponding site, to the extent that it does not allow either the type of vegetation covering the ground to be represented, or the communication means such as rivers, roads and railways, nor the built up areas for example.
To overcome this drawback, methods are known making possible the synthetic representation of relatively realistic landscapes, in which trees, constructions and superstructures appear in relief, further shown, like the ground, in colors so as to improve the readability thereof. These methods have however the drawback of being very unwieldly to use, for they require modelling of the whole of the landscape using colored facets, which, at the present time, can only be done manually and by a qualified operator. Furthermore when this costly modelling has been made, storage thereof occupies considerable room in the memory, which limits its application to small ground surfaces.
The invention overcomes the above drawbacks by providing a method of the above defined type, making possible the presentation of relatively complete information while remaining fairly simple to implement automatically, without manual intervention.